Subsea power cables are often brought from land to offshore installations such as oil platforms and wind turbines, in order to enable power transmission between land and sea. Such power cables are typically laid from land to the destination of installation by means of special cable laying marine vessels onto which the subsea power cable is loaded, for example onto a large cable carousel. The subsea power cable, which may have a weight of thousands of tons and a length of a number of kilometres, is successively rolled off the carousel and laid down on the ocean floor as the vessel travels towards the destination of installation.
In the process of bringing a subsea power cable offshore it may be necessary to control its axial movement and vertical position in certain situations. When the cable laying marine vessel has reached the destination of installation, it may for example be desirable to test the subsea power cable e.g. the optical transmission and power transmission capabilities of the subsea power cable, in order to ensure proper functioning prior to finalizing the installation. While performing the test, it is desirable to maintain the subsea power cable in a fixed position, in particular to restrict axial movement of the subsea power cable which may occur due to pulling forces from the weight of the majority of the subsea power cable submerged in the sea.
A second situation which could involve the necessity of controlling the axial movement of a subsea power cable is in the event that two subsea power cables are jointed offshore, for example when installing a very long subsea power cable which must be created from at least two joined subsea power cables.
For the situations mentioned above, tensioners arranged on the vessel, applying radial pressure to the subsea power cable may be used to fixate the subsea power cable. When installing a subsea power cable in deep-water i.e. depths of 500-1500 m, or ultra deep-water i.e. depths starting at 1500 m, it may however be necessary to apply very high radial forces to the subsea power cable by means of the tensioners. The high radial forces may result in that the subsea power cable becomes damaged.
A third situation which involves control of axial movement of a subsea power cable is when a subsea power cable is pulled from or onto a marine vessel, or when it is pulled onto an offshore platform for attachment to a hang-off. For this purpose, a Chinese finger is typically pulled onto the subsea power cable end, which can be coupled to a winch to enable axial movement of the subsea power cable. Chinese fingers may however not be able to hold the weight of a subsea power cable for installations in deep-water and ultra deep-water. Moreover, the installation of a Chinese finger may be cumbersome, and takes a considerable amount of time, which translates into higher costs and an increased risk of weather changes.